We propose to study intestinal calcium transport in an isolated intestinal cell system by investigating the quantitative effects of the addition of 1,25-(OH)2-vitamin D3 and of extracellular calcium induction of the calcium binding protein (CaBP) and on cellular calcium uptake. The results obtained so far accord with our hypothesis, namely that CaBP accumulation is regulated in part by a local, calcium-concentration dependent process. BIBLIOGRAPHIC REFERENCES: Dominick L. Cinti, Ellis E. Golub and F. Bronner. 25-Hydroxycholecalciferol: High Affinity Substrate For Hepatic Cytochrome P-450. Biochem. Biophys. Res. Commun. (1976, in press). Felix Bronner, Ellis E. Golub and Jan A. Fischer. The Effect of Vitamin D On Renal Calcium Clearance. Proc. Intern. Symp. on Urolithiasis Research (1976, in press).